There are several types of home thermostats from which a homeowner can choose. Each thermostat controls either the heat or air conditioning in a dwelling differently. Three main types of home thermostats include bimetallic element thermostats, mercury tube element thermostats, and bellows element thermostats. Home thermostats can be set manually by the occupants, or they can be programmed to go on and off at certain times.

Bimetallic element thermostats are among the most common types of home thermostats. Heat or air conditioning will either be turned off or on because of a coil made from two metals. As the temperature in the room fluctuates, the coil will either expend or contract. As it does this, it opens or closes contacts, switching the heat or air conditioning on or off.

Home thermostats with mercury tube elements also have a bimetal coil. On these coils, however, a glass tube filled with mercury, or liquid metal, works as a weight. As the coil expands or contracts, the mercury moves from one side of the tube to the other. This will either close or open a contact. If it tips in one direction, it will close a circuit to switch the heat on. If it tips in the other direction, it will open the circuit, turning the heat off.

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A home thermostat with a bellows element is filled with a volatile liquid, or a liquid that becomes vapor at a certain temperature. As this liquid is vaporized, the bellows expands. This then causes a circuit to close, switching on the heat or air conditioning. When it deflates, the circuit is opened, which causes the heat or air conditioning to switch off.

Many home thermostats are set manually by home owners. These usually include a dial that can be spun, or a lever that can be moved in one direction or the other. These home thermostats are very common, considering they are easy to install.

They are also much less expensive to buy. One disadvantage of these home thermostats, however, is the possibility of higher utilities. If these thermostats are not regularly controlled, the heat or air conditioning will be running while the occupants are away. This can result in wasted energy and higher gas or electric bills.

A programmable thermostat is usually a little harder to install. Although they are more expensive to purchase, they are often the most economical choice in the long run. Occupants can program these thermostats to switch on or off at a certain temperature. For example, if a person wants the heat turned down to a certain temperature on the days that he goes to work, he can program the thermostat once and forget about it. This can help minimize leaving the heat on when he will be away, especially if he is forgetful.

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